A HEMT (High Electron Mobility Transistor) of a 4-terminal structure has been proposed as a lateral switching device including a heterojunction structure in Non-Patent Literature 1.
In the proposed switching device, a heterojunction structure is formed by laminating an i-GaN layer and an i-AlGaN layer on a sapphire substrate or the like. A gate electrode of a MOS structure (hereinafter, referred to as a MOS gate electrode) is provided to reach the i-GaN layer by penetrating through the i-AlGaN layer. A source electrode and a drain electrode are provided on both sides of a surface of the i-AlGaN layer with the MOS gate electrode in between. A laminated structure of an i-GaN layer and a p-GaN layer is formed on the surface of the i-AlGaN layer between the MOS gate electrode and the drain electrode. A junction gate electrode (hereinafter, referred to as a JG electrode) is provided on a surface of the p-GaN layer. The i-GaN layer and the p-GaN layer provided on the i-AlGaN layer reach close proximity to the drain electrode by protruding in a direction to the drain electrode more than the JG electrode does.
The switching device of a 4-terminal structure is formed by disposing the JG electrode and the MOS gate electrode between the source electrode and the drain electrode in the manner as above.